1. Technical Field
This disclosure relates to all image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, for example, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting liquid droplets.
In such a liquid-ejection-type image forming apparatus, when liquid is not ejected from nozzles of the recording head for a long time, micro vibrating pulses (non-ejection pulses) may be applied to the head to vibrate the meniscus of liquid in the nozzles without ejecting liquid droplets from the recording head to maintain the condition of the nozzles.
For the micro vibrating of the recording head, for example, JP-2010-179531 proposes to apply different types of micro vibrating waveforms in response to the ejection rate of liquid.
To maintain the condition of the nozzles of the recording head, such an image forming apparatus may also perform, during printing, dummy ejection operation (also referred to as flushing operation) in which liquid droplets not contributing to image formation (dummy ejection droplets) are ejected from the nozzles of the recording head.
In addition, such an image forming apparatus may be a line-type image forming apparatus capable of printing images on a continuous recording medium, such as a rolled sheet of paper, a continuous sheet of paper, a continuous-form paper, or a web medium. In such a case, unlike a case where cut sheets are used as recording media, dummy ejection operation cannot be performed between recording media conveyed. Hence, the image forming apparatus performs one of first-type dummy ejection operation (referred to as line flushing operation) to perform dummy ejection per a certain length of the continuous recording medium or second-type dummy ejection operation (referred to as star flushing operation) to eject a less visible size of liquid droplets for dummy ejection on an image formation area of the recording medium. For example, JP-2008-213471 proposes such a line flushing operation.
For the line flushing operation of the line-type image forming apparatus using the continuous sheet, it is necessary to cut portions of the continuous sheet on which liquid droplets for dummy ejection are ejected. Therefore, it is disadvantageous in that a portion of recording media (cut portion) is wasted. However, it is advantageous in that liquid droplets for dummy ejection can be intensively discarded.
By contrast, for the star flushing operation, it is advantageous in that such a wasted portion of recording medium does not occur. However, since a less visible size of small droplets are discarded over an image formation area of a recording medium, the effect of discarding liquid droplets may not be sufficiently obtained in a less-humid condition or an image of a low printing duty.
In the dummy ejection operation, by discarding viscosity-increased liquid not used for image formation from nozzles, the nozzles are maintained in a state in which liquid droplets can be normally ejected from the nozzles, thus requiring waste of liquid ejected for dummy ejection. Therefore, it is preferable to minimize the waste of liquid and increase cost per performance (CPP).